Scientists aren’t entirely sure how life arose on Earth, but a popular theory is that the constant cycles of wet and dry conditions on land helped form the complex chemical building blocks necessary for microbial life. That’s why the mosaic of well-preserved old mud cracks found by NASA’s Curiosity rover is so exciting for the mission team.

A new article in the journal Nature details the distinctive hexagonal pattern of these mud cracks as the first evidence of wet and dry cycles occurring on early Mars.

“These particular mud cracks form when wet-to-dry conditions occur repeatedly—possibly seasonally,” said lead author William Rapin of the French Institute for Astrophysics and Planetology Research.

A close-up view of the panorama taken by Curiosity’s Mastcam in Pontura shows hexagonal patterns circled in red at right in the same image, showing these mud cracks formed after many wet and dry cycles over the years. -Caltech/MSSS/IRAP

Curiosity gradually climbs the sedimentary layers of Mount Sharp, which rises 3 miles (5 kilometers) into Gale Crater. The rover detected mud cracks after drilling a rock sample nicknamed “Pontur” in 2021, located in a transition zone between a clay-rich layer and an upper layer rich in salty minerals called sulfates. Clay minerals usually form in water, while sulfates tend to form when the water dries.

The minerals distributed in each region reflect different periods in Gale Crater’s history. The transition zone between the two marks a time when long dry periods began to prevail and the lakes and rivers that once filled the crater began to recede.

As the mud dries, it compresses and splits into T-joints, something Curiosity previously discovered in “Old Soaker,” a collection of mud cracks below Mount Sharp. These joints are evidence that the Old Socker mud once formed and dried, while the repeated water movement that formed the Pontur mud caused the T-joints to soften and become Y-shaped, eventually forming a hexagonal pattern.

The hexagonal cracks in the transition zone continued to form even as new sediment accumulated, suggesting that wet-dry conditions persisted for a long time. Curiosity’s precision laser instrument, ChemCam, confirmed a persistent sulfate crust along the edges of the cracks, which is not surprising given the proximity of the sulfate zone. It was the salty crust that made the mudcracks resistant to erosion and protected them for billions of years.

right conditions

“This is the first concrete evidence that the ancient climate of Mars had regular wet-dry cycles similar to those on Earth,” Rapin said. “But more importantly, wet-dry cycles are beneficial—perhaps even necessary—for the molecular evolution that could lead to life.”

While water is essential for life, a careful balance is required – neither too much nor too little water. The conditions that support microbial life—those that allow a long-lived lake, for example—are not the same as the conditions scientists believe are necessary to support the chemical reactions that can give rise to life. An important product of these chemical reactions are long chains of carbon-based molecules called polymers, including nucleic acids, molecules that are considered the chemical building blocks of life as we know it.

Wet-dry cycles control the concentration of chemicals that fuel the basic reactions that lead to polymer formation.

“This paper expands on the discoveries made by Curiosity,” said mission project scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in Southern California. “In 11 years, we found a lot of evidence that ancient Mars may have supported microbial life. Now the mission has found evidence of conditions that may have also contributed to the origin of life.”

The discovery of the Pontur mud cracks may have provided scientists with the first opportunity to examine the remains of the living cauldron. Earth’s tectonic plates are constantly reworking its surface, preserving examples of its prebiotic history. Mars has no tectonic plates, much older periods of the planet’s history have been preserved.

“We’re very lucky to have a planet like Mars soon that still has the memory of the natural processes that could have given birth to life,” Rapin said. Said. Source